1. Field of the Invention
The present invention relates to a method for manufacturing a package, a method for manufacturing a piezoelectric vibrator, and an oscillator, an electronic device, and a radio-controlled timepiece each having the piezoelectric vibrator.
2. Description of the Related Art
Recently, a piezoelectric vibrator utilizing quartz or the like is used in a cellular phone and a portable information terminal as the time source, the timing source of a control signal, a reference signal source, and the like. Although there are various piezoelectric vibrators of this type, an SMD-type piezoelectric vibrator is known as one example thereof. As the piezoelectric vibrator of this type, a three-layered piezoelectric vibrator in which a piezoelectric board having a piezoelectric vibrating reed formed thereon is interposed between a base board and a lid board is known. In this case, the piezoelectric vibrator is accommodated in a cavity (sealed space) that is formed between the base board and the lid board.
Moreover, in recent years, instead of the three-layered piezoelectric vibrator, a two-layered piezoelectric vibrator has also been developed. The piezoelectric vibrator of this type has a two-layered structure in which a base board and a lid board are directly bonded and packaged, and a piezoelectric vibrating reed is accommodated in a cavity formed between the two boards. The packaged two-layered piezoelectric vibrator is suitably used in that it is excellent in achieving a thin profile compared with the three-layered structure.
As a method of directly bonding the base board and the lid board which are made of a glass material, anodic bonding is proposed. For example, JP-A-2001-72433 disclosed an anodic bonding method that involves fixing a bonding material to an inner surface of one board, and then connecting a probe to the bonding material to be used as an anode, disposing a cathode on an outer surface of the other board, and applying a voltage between the bonding material and the cathode to bond the bonding material to an inner surface of the other board. As a material of the bonding material, Al is used.
However, there is a problem in that when the bonding material used for the anodic bonding is exposed to the outside of the bonded package, the bonding material made of Al will be corroded, and airtightness of the package will be degraded.
Therefore, in recent years, the use of Si as material of the bonding material has been investigated.
However, since the Si film has a large sheet resistance, when the thin bonding material is made of Si, the resistance value will increase. For this reason, when the probe is connected to the bonding material during the anodic bonding, a voltage drop will increase in proportion to a distance from a probe connection point. As a result, there is a problem in that the potential of the bonding material will be uneven, and anodic bonding is not achieved at positions distant from the probe connection point although anodic bonding is achieved near the probe connection point.
In order to achieve the anodic bonding at positions distant from the probe connection point, it is necessary to perform anodic bonding by applying a high voltage, which may however increase the amount of energy consumption.
In addition, in order to form a Si film having a low resistance value, it is necessary to form the Si film by sputtering, CVD, and the like at a high temperature (800° C. or higher). However, since the softening point of a glass board that forms the Si film is about 600° C., it is difficult to form the Si film on the glass board at a high temperature.